The present invention relates to fluid jet print heads and, more particularly, to a print head of the type in which jet drop breakup is stimulated by bending waves which travel along an orifice plate.
Ink jet print heads are known in which the print head defines one or more rows of orifices which receive an electrically conductive recording fluid, such as for instance a water base ink, from a pressurized fluid supply manifold and eject the fluid in rows of parallel streams. Printers using such print heads accomplish graphic reproduction by selectively charging and deflecting the drops in each of the streams and depositing at least some of the drops on a print receiving medium, while others of the drops strike a drop catcher device.
In one type of ink jet printer, as shown in U.S. Pat. No. 3,701,998, issued Oct. 31, 1972, to Mathis, the print head includes a manifold, defining a fluid receiving reservoir, to which is bonded a relatively thin orifice plate, defining the rows of orifices. The orifice plate is made of stainless steel or nickel coated beryllium-copper and is somewhat flexible. The orifice plate is bonded to the manifold at the periphery of the orifice plate such that it bridges and closes the manifold opening leading to the reservoir. As a consequence, the orifices in the orifice plate are in direct fluid communication with the reservoir.
As fluid is applied under pressure to the fluid receiving reservoir, it flows through the orifices and emerges from each orifice as a fluid filament. The fluid filament then breaks at its tip into a succession of fluid drops. Left to natural stimulating disturbances, the filaments would break up erratically into drops of various sizes at irregular intervals. As can be appreciated, in order to provide precise charging of the drops as they are formed, it is important that the drop breakup process be uniform and that drops of substantially constant size and spacing are formed in each stream.
In order to produce such uniform breakup of the fluid filaments, it is known to vibrate the orifice plate at one end with an electromechanical transducer, such as a piezoelectric transducer, thus producing a series of blending waves which travel along the plate. These waves cause each of the orifices to vibrate, producing pressure varicosities in the fluid filaments emerging from the orifices, and resulting in drops of relatively uniform size and spacing being formed from the fluid filaments.
It will be appreciated that it is desirable to be able to replace the print head in a printer during servicing without replacing the electromechanical stimulator transducer. A problem has been noted, however, in that the amplitude of the mechanical vibrations required for optimum stimulation has been found not to be uniform. Thus, stimulating each of a number of print heads with a transducer driven at a single vibrational amplitude level results in at least some of the print heads producing jet drop streams which are either over stimulated or under stimulated. As a consequence, installation of a replacement print head in the field has required that a technician making the installation monitor the breakup of the jets and adjust the driving signal to the transducer accordingly. This is somewhat difficult to accomplish in the field and, additionally, provides no assurance that optimum stimulation will be provided over an extended period of operation of the print head.
It has been seen, therefore, that there is a need for print heads which are readily interchangeable, and in which optimum stimulation is maintained over extended periods of operation of the print heads.